Changes Ruby 2.4 version to 2.4.0
Changes Ruby 2.4 version to 2.4.0

Seems like Travis is having problems with 2.4.1. See https://github.com/travis-ci/travis-ci/issues/7848; it's not the same issue, but concerning.

gamera-team/gamera,dobbs/gamera,dobbs/gamera,gamera-team/gamera